Method of fabricating indicator light with molded nylon jacket



y 3, 1960 F. A. HARRINGTON 2,934,792

METHOD OF FABRICATING INDICATOR LIGHT WITH MOLDED NYLON JACKET FiledJune 16, 1958 2 Sheets-Sheet l Ill/ll iNV ENT OR. FVANK A HARE/N6 TONifwyiil A aenEY- y 3, 1960 F. A. HARRINGTON 2,934,792

METHOD OF'FABRiCATING INDICATOR LIGHT WITH MOLDED NYLON JACKET FiledJune 16, 1958 2 Sheets-Sheet 2 quentlyreplaced as they outlive theiruseful life.

METHOD OFFABRICATING INDICATOR LIGH T WITH MOLDED NYLON JACKET Frank A.Harrington, Brea, Calif., assignor to Marco This application is in parta continuation of my pending application Serial No. 379,012, filedSeptember 8,

d953, for Indicator Light With Molded Nylon Jacket.

This invention relates to indicator lamps, such as are used forindicating to an operator or observer, the conditions of operation ofremotely located portions of an electrical system or anelectromechanical system. For

example, the instrument panel of a large airplane carries not only thecontrol actuators for many items of mecha nism utilized in controllingthe operation of the airplane, but also many indicator lamps forindicating the conditions of response and other conditions of operationof the various control units.

The lamp bulbs used for such indicator lamps are ordinarily quite small,but it is not customary to subject the eyes of the pilot or otheroperator to the direct rays of the lamp bulb. Rather, the usual practiceis to mount the lamp bulb in a casing having at its exposed end a capwhich carries a lens or window, usually of translucent material such asto dim the harsh glare of the direct rays of the lamp bulb, and quiteoften of a colored material (eg. the color red) to increase theefficiency of the indicator lamp in arresting the attention of theobserver.

Such lamps are used in large numbers and are fre- Accordingly, it is ofprime importance that they be of relatively inexpensive construction.

With the foregoing in mind, the primary object is to provide anindicator lamp of particularly inexpensive construction. In thisrespect, the invention contemplates a lamp comprising simply a smalllamp bulb and a jacket including a light dimming or light transmittinghood surrounding the forward portion of the bulb and which can besatisfactorily molded and to which it is easy to impart the desiredcharacteristic of translucency. I am aware that others have previouslyproposed the imolding of a lamp bulb into an integral jacket of plasticmaterial completely enclosing the same. However, such lamps aspreviously proposed have not been satisfactory, due to a number ofconditions including the difiiculty bulb at a temperature sufiicientlylow to avoid damaging the lamp bulb; and the difiiculty of too rapiddeterioration of the lamp bulb under the heat which is radiated by thelamp bulb when in use. Another problem is that of, avoiding crushing theextremely thin envelope of a small lamp bulb under the pressure ofinjection molding procedure.

Among the available moldable plastic materials that :can easily berendered translucent, the possibility of molding the lamp jackets out ofglass is obviously ruled of molding a suitable covering material arounda lamp 2,934,792 Fatented May 3, 1960 ice out because, at thetemperature at which molten glass can be satisfactorily injectionmolded, the thin envelope of the lamp bulb would be promptly melted andabsorbed into the body of molten glass, with a consequent completedestruction of the lamp bulb as a functional unit. As to the group ofsynthetic resin plastics, thermosetting materials (such as the phenolicaldehydes) which would have adequate resistance to deterioration undertemperatures and other conditions of usage, cannot be satisfactorilyinjection molded because they require too slow a molding cycle. Toattempt to cast the lamp bulb into such materials is unsatisfactory fora number of reasons, one of which is that the process is too expensive.

Some of the thermoplastic resins, of satisfactory translucencycharacteristics, can be satisfactorily injection molded, but are notcapable of withstanding the ambient temperatures of operation ofindicator lamps. Others require too high a molding pressure, such aswould crush .the thin envelope of the lamp.

As to the foregoing problems, the invention has as its object to providean indicator lamp which .is inexpensive; which can be satisfactorilyprocessed by injection molding; which is adequately resistant to thedeteriorating effect of ambient operating temperatures, vibration, etc.;which is otherwise sufficiently durable; and to which can be imparted asatisfactory translucency and finish.

Another problem that has been met with in the attemps to injection molda translucent jacket .around .a small lamp bulb, is the difficulty ofobtaining a symmetrical coaxial relation between the lamp bulb and theexternal wall of the jacket in the final molded product. In injectionmolding processes, the plastic material is injected under substantialpressures. Such pressures tend to displace the lamp bulb to an eccentricposition in the mold. Obviously, a lamp jacket which is too thin on oneside and too thick on an opposite side would be unsatisfactory,particularly where the material is of such a translucency as tosubstantially dim down the intensity of the light rays. The dimmingeffect is obviously related to the thickness of the jacket wall, andsuch thickness must be uniform in order to obtain a jacket ofcircumferentially uniform dimming effect. Likewise, in those caseswherein a substantially transparent jacket might be desired, anysubstantial difference in thickness of the jacket wall around itscircumference, would be definitely noticeable and thereforeobjectionable. It would be objectionable for the further reason that thethin envelope of the lamp bulb would not have the same uniform supportaround its circumference as in the case of a jacket of uniform wallthickness.

A further object of the invention therefore is to provide an indicatorlamp embodying a lamp bulb molded into an integral packet of uniformwall thickness circumferentially, i.e. uniform radial thickness. Anotherobject is to provide an improved method of molding such a jacketed lampbulb.

Other objects will become apparent in the ensuing specifications andappended drawings in which:

Fig. 1 is a side view of an indicator embodying my invention; a

Fig. 2 is an axial sectional view thereof;

Fig. 3 is an end view of the base of the lamp; i

Fig. 4 is a transverse sectional view on the line 44 of Fig. 2;

Fig. 5 is a sectional view of .a portion of an injection moldingapparatus, with the internal components of an indicator lamp of myinvention installed therein, ready for the injection molding operation;

Fig. 6 is a fragmentary axial sectional view of a lamp embodying amodified form of the invention;

central body portion of envelope 12.

Fig. 7 is a fragmentary axial sectionalview of a lamp embodying amodified form of the spacer spider;

Fig. 8 is a perspective view of another modified form of the spacerspider;

Fig. 9 shows another modified form of the spider;

Fig. 10 shows another modified form of the spider;

Fig. 11 is a plan view of a mold utilizing a modified form of myimproved molding method; and

. Fig. 12 is a crosssectional view taken on the line 12-12 of Fig. 11.

The invention as disclosed in Figs. 1-4

Referring now to the drawings in detail, the indicator lamp which isshown in Figs. l4 as an example of one form in which the invention maybe embodied, comprises generally a lamp bulb A and an integral, moldedjacket B, the latter including a light ray transmitting hood 10 and abase 11.

The lamp bulb A includes a thin envelope 12, which normally will be ofglass, a stern portion 13 in which a pair of conductors 14, 14 areanchored and sealed; and a suitable light generating or emitting element15 connected to and supported by the upper ends of one or both of theconductors 14, 14. The particular lamp bulb shown is of theglow-discharge type (e.g. a neon tube) and the element 15 which isvisible in Fig. 2, in this case constitutes one of the electrodesconstituting a conductive connection to the gas filled atmosphere withinthe tube. In a filament type lamp bulb, it would of course be replacedby a filament. Connected to the respective conductors 14, 14 are a pairof terminals in the form of legs 16, 16' which are disposed in parallelrelationship, properly spaced for insertion into the apertures of anelectric outlet receptacle or for direct soldered connection toconductor wires.

The hood 10 of jacket B includes a tubular lateral wall portion 18 ofuniform radial thickness surrounding the In the particular lamp shown,this central body portion of the envelope 12 is cylindrical and thelateral wall portion 18 of the jacket is correspondingly cylindrical.The hood 10 also includes a closed end portion 19 which, for bestappearance and dispersal of light rays, may be spherical or spheroidal.

Base 11 of the jacket B includes a waist portion '21 which may bepolygonal in transverse section, so as to provide fiat wrenching faces21 for engagement by a wrench to hold the lamp while it is being securedinto a mounting panel or the like. The base 11 also includes anexternally threaded end portion 22 upon which is threaded a nut 23 forclamping a washer 24 against the rear face of a mounting panel.

Conductors 14, 14' and terminal legs 16, 16 are molded into the threadedend portion 22, in a symmetrical relation to the longitudinal axis ofthe lamp, and the end portions of legs 16, 16 project from base 11, forinsertion into an electrical connector socket or for soldered connectionto conductor wires.

Intermediate the base 11 and hood 1t}, jacket Bhas a waist flange 25within which is molded a spider 26 of Nylon material. Spider 26 (Fig. 4)has a central circular aperture 27 which receives the cylindrical bodyportion of lamp bulb envelope 12 adjacent the lower extremity thereof,the edge of the spider surrounding the aperture being snugly engagedagainst the wall of envelope 12. Spider 26 is of star form, having aplurality of radiating arms 28 which project into waist flange 25.Circumferentially spaced notches or gaps between the arms 28 are filledby web portions 29 of jacket B which bridge between the base 11 and hood10, integrally joining them.

The molding process of Fig. 5

The primary function of spider 26 is to secure the envelope 12 inacoaxial position \vithin'a mold cavity 31 (Fig. 5) during the moldingprocess. Fig. 5 illustrates a mold comprising a sectional female die 32having the cavity 31 therein, and a closure section 33 having thereindeep, narrow recesses 34 to snugly receive the legs 16, 16'. Mold cavity31 includes an annular waist recess 35 in which the fingers 28 of spider26 are received.

The plastic material is injected into the mold through a central port 37at the crown of the mold cavity and through a plurality of lateral ports38 disposed equidistantly around the circumference of the cavity. Fromthe upper portion of the cavity, wherein hood 10 is molded, it flowsfreely through the gaps between the fingers 28 of the spider 26, intothe base portion of the cavity, to form the base 11.

In a preferred form, spider 26a (Fig. 8) includes ciricumferentiallyspaced fingers 41 projecting generally axially from its inner margin atthe upper side thereof, and slightly converging so as to engage the lampbulb with light, yielding pressure; thus securely grasping the bulbwithout any likelihood of crushing the envelope 12.

Modified formFig. 7

extent as to avoid either blocking or deflecting the light rays to anydifferent degree than the body of the jacket.

Modified molding meth0dFig. 11

Fig. 11 illustrates a simplified and improved molding method whichemploys a mold comprising mating die blocks 32a, 32b 'conjointlydefining a mold cavity 31a and having respective locating pins 43 andbores 44 for accurately matching the die blocks to one another. In-

stead of the lateral injection ports 38 of Fig. 5, the apparatus has asingle injection port 38a, coaxial with the major axis of mold cavity31a and communicating with the end of the cavity in which the base ofthe lamp is shaped.

Bulb A is positioned in the mold cavity by engagement of its terminallegs 14a in slots 45 formed sectionally in the mold blocks 32a, 32b; andby engagement of its tapered nose 46 in a conical end recess 47 ofcavity 31a, which is symmetrically contoured about the major axis of themold cavity.

Cavity 31a has, intermediate its ends, an annular waist recess 35a forshaping the waist flange 25a of the lamp jacket; and an internallythreaded base-forming recess 48 for shaping the threaded cylindricalbase 22a of the lamp.

In the improved process of molding utilizing the mold of Figs. 11 and12, a bulb A is inserted in the lower mold block 32b, terminal legs 14abeing fitted over block 32b,

the mold is clamped shut, and plastic nylon resin mate- 'rial isinjected under pressure through injection port 38a. ,As the fiowiugresinmeets the rear end of bulb A, it forces the bulb A forwardly until itsnose 46 hottoms in recess 47, thereby accurately centering the bulb A inthe mold cavity at its forward end. The terminal legs 14a, slidingsnugly in slots 45, maintains the rear end of bulb A centered on themajor axis of the mold cavity. As the flowing resin advances toward theforward end of the mold cavity, it parts and flows equally around allsides of bulb A.

Thus the jacket B which is molded around bulb A, is

symmetrically disposed around the bulb in coaxial relation and ofuniform wall thickness throughout its circumference.

I have discovered that the nylon molding material has the combination ofcharacteristics which makes it entirely suitable for solving the severalproblems noted hereinabove. It has a relatively low molding pressure(e.g. in the neighborhood of 1500 pounds p.s.i., which is considerablybelow a pressure that could be damaging to the relatively fragileenvelope of the lamp bulbs utilized by the invention). This is incontrast to the average molding pressures of commonly used injectionmolding plastic materials, which range in the neighborhood of 15,000p.s.i., a pressure entirely too great to be withstood by the fragileglass envelope of the lamp bulb. Also, the nylon material is relativelystable in the presence of ambient operating temperatures for mostconditions of usage of indicator lamps of the type under consideration.Such operating temperatures commonly range in the neighborhood of 350 F.and the known thermoplastic materials which could be successfullyinjection molded about the thin glass envelope of the lamp bulb, willnot satisfactorily hold up under such operating temperatures, but willrapidly deteriorate.

I claim:

A method of fabricating an indicator lamp including a lamp bulb, amolded jacket enclosing the same, and a pair of terminal legs projectingfrom the rear end thereof and electrically connected to said lamp bulb,including the following steps: providing a sectional mold having a moldcavity corresponding to the external contours of the jacket to be moldedand having a pair of spaced slots to receive the said terminal legs soas to provide one point of support for said lamp bulb; inserting saidbulb into said mold with said terminal legs received in said slots toposition the rear end of the bulb in concentric relation to the mold;piloting the forward end of the bulb in the forward end of the moldcavity; injecting polyamide molding resin into the rear end of the moldalong the major axis of the mold and around said bulb to fill the moldcavity; utilizing the pressure of the resin against the rear end of saidbulb, as

it enters the mold, to press the forward end of the bulb' against theforward end of the mold cavity with a centering action to establishconcentricity of the forward end of the bulb on the major axis of themold; and causing the resin to solidity to form a concentric jacketabout the bulb.

References Cited in the file of this patent UNITED STATES PATENTS1,995,863 Prideaux Mar. 26, 1935 2,076,412 Oldham Apr. 6, 1937 2,433,373Krim Dec. 30, 1947 2,604,660 Karns July 29, 1952 2,504,661 Karns July29, 1952

